Development of oil and gas fields in relatively deep sea waters has resulted in a proliferation of pipelines connecting facilities to each other and to shore facilities. Many of these pipelines are at depths which are deeper than those at which divers can work. The pipelines are expected to have long service lives, but eventually dropped objects, mud slides, corrosion damage, material flaws or other failure mechanisms will affect these pipelines and require repair or replacement. Acceptable methods to perform repairs on these pipelines are not currently available.
U.S. Pat. Nos. 4,234,268 and 4,444,528 disclose methods to sever and lift subsea pipelines to the surface, but handling of the pipelines by surface ships is not addressed. Pipelines can therefore be recovered from the sea floor to surface vessels, but existing surface vessels have facilities to handle only one pipe. Repairing a pipeline by a method which includes lifting the pipe to the surface from both directions of the pipeline could not be easily accomplished by the prior art. It is therefore an object of the present invention to provide an apparatus and a method which is useful in repairing subsea pipelines wherein two ends of the pipe can be suspended, raised and lowered from a surface vessel, and the surface vessel can maneuver around the pipelines without changing the position of the pipelines relative to each other. It is a further object to provide such a method and apparatus wherein pipeline appurtenances such as anodes and hang-off clamps can be raised and lowered from the ship. It is a further object to provide such an apparatus and method which can be readily adapted for use from different existing pipeline-laying ships.